Warburg Pincus said Monday it raised its stake in MBIA Inc. to 25 percent, after the bond insurer posted a sharply smaller loss for the fourth quarter.

Warburg Pincus upped its stake from 20.2 percent, according to a Securities and Exchange Commission filing. The company has been investing hundreds of millions of dollars in MBIA since 2007 to help protect the company's financial-strength rating.